Objectives of the proposed research are: a. To explore mechanisms of active membrane transport of organic cations such as choline, catecholamines and drugs. b. To analyze further the mechanisms involved in bidirectional renal tubule transport of choline using the isolated perfused tubule of rabbits in collaboration with Dr. Francoise Roch-Ramel. c. To Investigate in the isolated tubule the previous finding that small loads of other cations will enhance the excretion of choline, e.g., lysine. d. To investigate the direct effects of the cation choline on the tubular transport of inorganic ions particularly Na positive, K positive, Cl negative, HCO3 negative, HPO4 negative and NH3 positive and also water using the Sperber technique. e. To similarly investigate the effects of catecholamines to detect an effect directly on transport of ions in contrast to circulatory effects. f. To study the effect of the carboxylic ionophore 537A-Lasalocid- on tubular transport of inorganic cations such as Na, K, Cl, HCO3 and on organic cations such as catecholamines and choline.